Phoenix-area heat wave ushers in ozone season

Residents urged to take steps to curb pollution

Maricopa County's ozone season starts today with a fresh burst of heat and sunlight, two key ingredients needed for unhealthful levels of the smog to form.

Temperatures could rise to nearly 100 degrees today as a strong high-pressure system creates the ideal conditions for ground-level ozone. The other elements - vehicle exhaust, power-plant emissions, gasoline, paint and industrial solvents - are always in abundant supply.

Ozone levels already were climbing late Thursday as the heat wave developed, and officials predicted the pollutant would reach moderate levels later today, although no ozone-related health advisories are expected.

Ozone pollution can form year-round, but it is most common from April through September, when the intense heat and sunlight are sustained and react with exhaust and other volatile compounds. During those months, ozone season, air-quality agencies increase efforts to educate people about the health risks of ozone and what they can do to lower smog levels.

"Ground-level ozone is something we can control," said Holly Ward, spokeswoman for the Maricopa County Air Quality Department. "We can control the number of times we get into our car to drive unnecessary trips. We can choose to refuel after dark."

Some other ways people can reduce ozone pollution are to carpool or telecommute, limit the time a car engine idles, reduce the use of gas-powered yard equipment and schedule big painting projects during cooler months.

The county has tried to reduce ozone pollution for years but has struggled to meet the federal standards. The desert's heat produces more ozone, and weather conditions trap it in the air. But much of the problem can be traced to the region's rapid growth, which has increased the number of vehicles on the road and added to other pollution-contributing activities.

Although state and county officials have submitted a plan to reduce pollution levels, the region is in violation of the existing standard of 75 parts per billion, as measured over an eight-hour period. The county exceeded that standard on 10 days during 2010.

The U.S. Environmental Protection Agency is reviewing a proposal to further reduce the allowable ozone levels to between 60 and 70 ppb. At the highest level in that range, Maricopa County would exceed the standards even more frequently; at some of the lower levels in the range, many areas of rural Arizona, including Yuma, Gila, La Paz and Navajo counties, could fail to comply based on three-year averages the EPA uses to compute ozone levels.

Vehicle-exhaust and power-plant emissions contribute to ozone levels in some of those areas, but rural officials say some of the pollutants are carried to their communities by the wind, a factor the EPA acknowledges. Those smaller counties say they could not afford to monitor ozone or impose programs such as emissions testing for cars and trucks.

Elected officials and business lobbyists nationwide have urged the EPA not to adopt such strict standards, and the agency has postponed its final decision several times. A new limit is now set to be announced in July, but opponents are fighting to further delay any action.

"Each time the standard is lowered, you have to put more controls in place," Ward said. "We are having a hard time meeting the current standard. So, should that go lower, we know we could be in trouble."

If an area consistently exceeds limits and fails to reduce pollution levels, the EPA can impose a federal plan and withhold highway funding.

Scientists say the evidence is clear that ozone can cause health problems, making it more difficult for people to breathe. It can cause coughing and shortness of breath and can increase the frequency of asthma attacks. It also can increase health risks among people with heart and lung ailments.

New research released by the EPA last month suggested that long-term exposure to ozone could result in more premature deaths.

Ozone also can interfere with the ability of some plants and trees to produce and store food and can make some plants more vulnerable to disease, insects or harsh weather.